Chemical Properties of Portland Cement

Loss on ignition and insoluble residue are the two chemical properties of cement.

1. Loss of Ignition

Due to the ignition of cement at a high temperature, loss in weight occurs due to the evaporation of moisture and carbon dioxide, which are present in combination with free lime or magnesia. Loss in weight is a measure of the freshness of cement. Hydroxides and carbonates of magnesium and lime do not contain any cementing properties; thus, they are called inert substances. The quality of cement will be better if the inert materials are lesser, and hence lesser will be the loss in ignition. Normally, the loss is around 2% and should not be more than 4%.

2. Insoluble Residue

An inactive part of cement is called the insoluble residue. It is determined by a simple test.

One gram of cement with 40 ml of water and 10 ml of concentrated HCL is stirred. The stirred mix is boiled at constant temperature for 10 minutes. Lumps if any are broken and the solution is filtered. The residue on the filter is washed with Na₂Co₃ solution, water and HCL in this order and finally again with water. The filter paper is dried, ignited and weighed to give an insoluble residue. Lower the percent of residue better is the cement. The maximum allowable value is 0.85%.